1. Field of the Invention
It is estimated that approximately 25% of our harvested fruits and vegetables are lost to postharvest diseases. In the past, synthetic chemical fungicides were relied upon for the control of such diseases; however, as concerns over the health risks posed by these chemicals have increased, many of them have been withdrawn from use by regulatory agencies as well as a result of consumer pressure. In addition, an increased resistance to fungicide treatment by the pathogens responsible for postharvest diseases has been observed. Thus, there is a strong incentive to develop safe and effective alternatives to chemical fungicides. This invention relates to a composition which provides such an alternative by utilizing an antagonistic microorganism (Candida saitoana) in combination with the sugar analog, 2-deoxy-D-glucose (2-DG).
2. Description of the Prior Art
The biological control of postharvest diseases by antagonistic microorganisms has become increasingly important with the advent of tighter controls on the use of chemical additives on agricultural food commodities. As a result, a number of investigators have applied compositions containing such microorganisms to agricultural commodities with some success.
The bacterium Bacillus subtilis has been shown to inhibit a variety of diseases such as brown rot (Monilinia fructicola) on peaches and other stone fruit and brown rot, gray mold rot (Botrytis cinerea) and bitter rot (Glomerella cingulata) on apples (Pusey et al, U.S. Pat. No. 4,764,371, 1988, and Pusey, U.S. Pat. No. 5,047,239, 1991). Pichia guilliermondii (anamorph Candida guilliermondii) was shown to be effective against a number of pathogens including Botrytis cinerea, Pencillium expansum and Alternaria alternata (Wilson et al., U.S. Pat. No. 5,041,384, 1991). McLaughlin et al. (Phytopathology, 1990) and Wilson et al. (Scientia Horticulturae, 1993) also have shown that various strains of Candida sp. were effective against Botrytis cinerea and Pencillium expansum in apples. A review of biocontrol technology was presented by Wilson and Wisniewski (Ann. Rev. Phytopathol., 1989). In addition to the use of microorganisms, the use of sugars and sugar analogs has also recently been investigated for application as fungicides on agricultural commodities (El -Ghaouth and Wilson, unpublished results). The antifungal property of sugar analogs is well documented; however, few attempts had been made to utilize them as fungicides (Barnett and Lilly, Science, 1951; Atkin et al., Ann Appl. Biol., 1964). The antifungal activity of 2-DG in particular has long been known (Johnson, J. Bacteriology, 1968; Biely et al., J. Bacteriology, 1971; Zonneveld, Developmental Biology, 1973); however, exploitation of this property for the inhibition of postharvest diseases on fruits and vegetables was not attempted.
Although biological control agents have proved safe and effective, the antagonistic effect has often fallen short of that achieved by chemical fungicides. A search for improvements has therefore continued in order to obtain biological control equal to, if not better than, that obtainable by chemical means.